1. Field of the Invention
The present invention relates to a test indicator.
2. Description of Related Art
There has been known a test indicator (called as a lever type dial gauge) (for example, JP 2008-309687 A). A test indicator is used to measure a minute displacement, such as circumferential deflection, total deflection, flatness, and parallelism, and for a precise comparison inspection, such as a machining error of a machined product with respect to a master work (or a block gauge).
A test indicator 100 includes a gauge head 3 rotatably supported about an axis by the body case. The gauge head 3 includes a contact ball 31 at the tip end thereof. Then, the displacement of the contact ball 31 is increased using the principle of lever. Thus, the test indicator 100 is a measurement device having high precision and high resolution.
Due to the structural character that the displacement (rotation displacement) of the gauge head 3 which rotates around the rotation axis is increased using the principle of lever, there is a point of attention when the test indicator 100 is to be used.
That is, the gauge head 3 needs to be parallel to a measurement target surface W as much as possible to perform measurement.
For example, the flatness of the measurement target surface W is to be measured. In this case, while the contact ball 31 is being in contact with the measurement target surface W, both are relatively moved. However, in order to correctly measure the unevenness (or roughness) of the measurement target surface W, the measurement target surface W is to be substantially parallel to the gauge head 3, and the angle between the measurement target surface W and the gauge head 3 to be substantially zero as illustrated in FIG. 1A. When the measurement is performed as illustrated in FIG. 1A, the displacement direction of the contact ball 31 coincides with the unevenness direction of the measurement target surface W to be measured. (The displacement direction of the contact ball is the normal line direction of the measurement target surface.)
On the other hand, when the gauge head 3 is not parallel to the measurement target surface W and the angle θ between the measurement target surface W and the gauge head 3 is large as illustrated in FIG. 1B, the displacement direction of the contact ball 31 does not coincide with the unevenness direction of the measurement target surface W.
(The displacement direction of the contact ball 31 is inclined with respect to the normal line direction of the measurement target surface W.)
In this case, the measurement value does not correctly reflect the unevenness of the measurement target surface W.
If (for some reasons) the test indicator 100 needs to be installed as illustrated in FIG. 1B, the unevenness of the measurement target surface W can be obtained by correcting the measurement value according to the angle θ.
Note that, the inclination of the test indicator 100 itself does not matter. As illustrated in FIG. 2A, although the test indicator itself is inclined with respect to the measurement target surface W, the gauge head 3 is only required to be substantially parallel to the measurement target surface W.